When it comes to landscape design and architecture, natural, real rock retaining walls are often considered the pinnacle of classic, timeless design and aesthetics. These types of walls, often constructed from natural flagstones, boulders or quarry stones, have been dry stacked or mortared together for many years, but require considerable skills to be of a steady durable construction. Moreover, natural stone walls are expensive to build, as natural stones are costly and the process of fitting the random stone pieces into a tight, coherent mass is time consuming and require an experienced craftsman.
Due to the popularity of the natural stone look, attempts have been made to reproduce it with manufactured retaining wall product. Two processes are currently known in the manufacture of such blocks: dry-cast blocks and wet-cast blocks. Dry-cast blocks are made using a combination of a concrete mix with very low water content, and a steel mold where large compression/vibration forces are used to compact the dry concrete mixture. On the other hand, wet-cast blocks are generally made by pouring concrete into a stiff or flexible mold that is open on top, and then leaving the concrete inside the mold for a curing period. However regardless of the method used to manufacture these blocks a true random stacking appearance has not been achievable. This is partly due to the following reasons:                1) Interlock system: Segmental retaining walls require some type of vertical interlock or shear resistance between the courses. Therefore, predetermined laying patters are required in order for the male interlock (pin, knob or lug) of the lower course to find the corresponding female core or slot in the upper course. As such, random stacking patterns are often not possible.        2) Block Size: Due to above-described reasons, the size (face width) of the blocks made according to the existing solutions, are limited to 2-3 different dimensions. Even with this limited number of face widths, specific laying patterns are required in order for the blocks to fit together and not result in a conflict between the vertical interlock of the block in the lower course and the core of the block in the upper course.        
Most dry-cast segmental retaining wall blocks have some type of vertical shear connection system to align the blocks in the wall, and prevent lateral earth forces from dislodging individual courses from the wall. Common types of connection include the tongue and groove system, the lug and core system, and the inclusion of multiple cores or grooves which require the installer to use an additional pin or clip to connect the blocks.
The above-mentioned types of connection are possible for retaining wall blocks manufactured using the dry-cast process as it allows the casting of shapes into both the bottom and the top surfaces of the block. As such, matching positive and negative shapes, or matching cores or grooves, can be cast into the top and bottom of the blocks to achieve an integral vertical interlock between the blocks located in the different courses.
However, the downside of the dry-cast process is that the textures created are very limited since the process involves the use of a steel mold which “eject” the product vertically after the vibration and compression cycle. Thus, the vertical faces of the resulting block cannot have any texture that is not in line with the vertical direction in which the product is “ejected”. Even when a dry-cast facing panel is realised and textured with a specialized press head, the look is still limited to the patterns or shapes created by a small number of the dry-cast press heads. Moreover, the depth of the false joints (which are typical to the look of a natural stone wall) is limited to the depth that the press head can reasonably reach by compression force.
Therefore, in order to achieve a true simulated rock texture, the blocks need to be manufactured using a wet-cast process as only more flexible molds can recreate the intricate detailing and texture of natural materials such as rocks.
However, the process of wet casting a concrete block, by its nature, has certain limitations. As previously explained, wet casting implies that concrete is poured into a mold that is open on top. Consequently, simulated texture can be cast on the sides and bottom of the blocks, but the top surface of the mold (which corresponds to the bottom surface of the corresponding manufactured block) remains open, and therefore cannot be textured or shaped as it is not contained. This poses a problem when it comes to the creation of an integral vertical connection system between wet-cast segmental retaining wall blocks. Since no shape can be cast into the bottom surface, current wet-cast blocks either do not have a connector system (and require the craftsman to secure them with adhesive) or have a rear lip system, this system requiring that only one surface be cast.
The drawback associated with walls constructed using blocks having a rear lip as vertical interlock system is that, when stacked, these blocks end up setting back each successive course of a distance equal to the thickness of the rear lip. This built-in set back is not always desirable, as vertically aligned walls (which require a vertically aligned connector system) are preferable for smaller landscape type walls, for example.
Hence, in light of the aforementioned, there is a need for an improved wet-cast concrete segmental retaining wall block which, by virtue of its design and components, would be able to overcome or at least minimize some of the above-discussed prior art concerns.